Fall 2010
Anderson
Mer231 – Thermodynamics I - Study Guide for Exam #2
This exam will cover Chapters 4, 5 and 6, however the material in this course is cumulative so you also need to
understand all the material from the first exam.
Part 1 of the exam will be closed book/closed notes. Part 2 will be open book/closed notes. You may also bring
1 8.5 by 11” sheet of equations.
The following is a summary of topics in each chapter that you need to understand for this midterm. Please
review and come see me if you do not understand the concepts. You should also review all example problems,
in-class problems and homework problems.
Note: these summaries are slightly modified version of the end of chapter summaries in your book! Make sure
that you understand what is listed below and review the Key concepts and Formulas at the end of every chapter.
Chapter 4 Summary (from Borgnakke and Sonntag, p 113, Note: Highlighted text is new) Work and heat are
energy transfers between a control volume and its surroundings. Work is energy that can be transferred
mechanically (or electrically or chemically) from one system to another and must cross the control surface either
as a transient phenomenon or as a steady rate of work, which is power. Work is a function of the process path as
well as the beginning state and end state. The displacement work is equal to the area below the process curve
drawn in a P-V diagram in an equilibrium process. A number of ordinary processes can be expressed as
polytropic processes having a particular simple mathematical form for the P-V relation. Work involving the
action of surface tension, single- point forces, or electrical systems should be recognized and treated separately.
Any nonequilibrium processes (say, dynamic forces, which are important due to accelerations) should be
identified so that only equilibrium force or pressure is used to evaluate the work term.
Heat transfer is energy transferred due to a temperature difference, and the conduction, convection, and
radiation modes are discussed.
You should be able to:
 Recognize force and displacement in a system.
 Understand power as the rate of work (force x velocity, torque x angular velocity).









Know that work is a function of the end states and the path followed in a process.
Calculate the work term knowing the P-V or F-x relationship.
Evaluate the work involved in a polytropic process between two states.
Know that work is the area under the process curve in a P-V diagram.
Apply a force balance on a mass and determine work in a process from it.
Distinguish between an equilibrium process and a non-equilibrium process.
Recognize the three modes of heat transfer: conduction, convection, and radiation.
Be familiar with Fourier’s law of conduction and its use in simple applications.
Know the simple models for convection and radiation heat transfer.
 Understand the difference between the rates ( W , Q ) and the amounts (1W2, 1Q2) of work.
Chapter 5 Summary (from Borgnakke and Sonntag, p 160) Conservation of energy is expressed for a cycle,
and changes of total energy are then written for a control mass. Kinetic and potential energy can be changed
through the work of a force acting on the control mass, and they are part of the total energy. The internal
energy and the enthalpy are introduced as substance properties with the specific heats (heat capacity) as
derivatives of these with temperature. Property variations for limited cases are presented for incompressible
states of a substance such as liquids and solids and for a highly compressible state as an ideal gas. The specific
Fall 2010
Anderson
heat for solids and liquids changes little with temperature, whereas the specific heat for a gas can change
substantially with temperature. The energy equation is also shown in a rate form to cover transient processes.
You should be able to:













Recognize the components of total energy stored in a control mass.
Write the energy equation for a single uniform control mass.
Find the properties u and h for a given state in the tables in Appendix B.
Locate a state in the tables with an entry such as (P, h).
Find changes in u and h for liquid or solid states using Tables A. 3 and A. 4 or F. 2 and F. 3.
Find changes in u and h for ideal- gas states using Table A. 5 or F. 4.
Find changes in u and h for ideal- gas states using Tables A. 7 and A. 8 or F. 5 and F. 6.
Recognize that forms for Cp in Table A. 6 are approximations to what is shown in Fig. 5.11 and the
more accurate tabulations in Tables A. 7, A. 8, F. 5, and F. 6.
Formulate the conservation of mass and energy for a control mass that goes through a process involving
work and heat transfers and different states.
Formulate the conservation of mass and energy for a more complex control mass where there are
different masses with different states.
Use the energy equation in a rate form.
Know the difference between the general laws as the conservation of mass (continuity equation),
conservation of energy (first law), and the specific law that describes a device behavior or process.
Understand the assumptions used when applying the conservation of mass and conservation of energy
equations to solve control mass problems.
Chapter 6 Summary (from Borgnakke and Sonntag, p 215) Conservation of mass is expressed as a rate of
change of total mass due to mass flows into or out of the control volume. The control mass energy equation is
extended to include mass flows that also carry energy (internal, kinetic, and potential) and the flow work needed
to push the flow in or out of the control volume against the prevailing pressure. The conservation of mass
(continuity equation) and the conservation of energy (first law) are applied to a number of standard devices. A
steady- state device has no storage effects, with all properties constant with time, and constitutes the majority
of all flow- type devices. A combination of several devices forms a complete system built for a specific purpose,
such as a power plant, jet engine, or refrigerator. A transient process with a change in mass (storage) such as
filling or emptying of a container is considered based on an average description. It is also realized that the start
up or shut down of a steady state device leads to a transient process.








Understand the difference between a control mass and a control volume
Understand the physical meaning of the conservation equations. Rate = in - out.
Understand the concepts of mass flow rate, volume flow rate, and local velocity.
Recognize the flow and non-flow terms in the energy equation.
Know how the most typical devices work and if they have heat or work transfers.
Have a sense about devices where kinetic and potential energies are important.
Analyze steady-state single-flow devices such as nozzles, throttles, turbines, or pumps.
Extend the application to a multiple- flow device such as a heat exchanger, mixing chamber, or turbine,
given the specific setup.
 Apply the conservation equations to complete systems as a whole or to the individual devices and
recognize their connections and interactions.
 Recognize and use the proper form of the equations for transient problems.
Fall 2010
Anderson
 Be able to assume a proper average value for any flow term in a transient.
 Recognize the difference between storage of energy (dE/dt) and flow (m h)
 Understand the assumptions used when applying the conservation of mass and conservation of energy
equations to solve control volume problems.
Some (but perhaps not all) things I expect you know (i.e. for the closed portion of the test)



Simple statement of COE for a Control Mass: Q  E  W
Simple statement of SSSF COM for a Control Volume:  m in   m out
Simple statement of SSSF COE for a Control Volume:
Q   m (h  KE  PE ) in  W   m (h  KE  PE ) out

You should be familiar with the USUF equations but you don’t need to memorize them.

The definition of Kinetic Energy: KE  1 2 mV 2












The definition of Potential Energy: PE  mgz
The difference between internal energy and enthalpy.
Understand how to apply assumptions to the solution of control mass and control volume problems
Ideal Gas Law
Definition of quality x = mv/mtotal
How to calculate specific volume, internal energy and enthalpy using quality.
How to calculate the forces acting on a piston.
Know how to apply the definition of work (i.e. W = ∫Fdx).
The definition of moving boundary work and how to calculate it (i.e. W = ∫PdV).
How to draw P-v, P-T and T-v diagrams, identify states and processes on those diagrams.
How to read the property tables.
Definition of all the “bolded” items above.